Proper siting and installation of the tree. Planting Lemon Trees in Your Yard lays out all the details about the type of soil and exposure lemons require and will tell you how to get your tree off to a good start.

Proper
watering. A newly planted lemon tree should never be exposed to
drought conditions but you do not want to keep it as wet as you would
most other evergreen trees.Citrus roots need more air than the roots of most other trees in order to survive. Water displaces air in the soil. Your
lemon tree's roots will rot in constantly moist soil. Let the soil dry
to a depth of about an inch and then water it thoroughly.Avoid
frequent light sprinklings that only wet the surface of the soil. This
practice causes tree roots to grow up toward the surface rather than
down and out the way you want them to. You

end up with a shallowly rooted tree that has zero drought tolerance and will fall in a storm.

Winter Lemon Tree Care

Here in central Florida, I see people going to a lot of trouble protecting lemon trees in winter. Some people wrap the tree in plastic and place a light bulb underneath it.

Some people enshroud their trees in blankets and quilts.

Some wrap Christmas lights up the trunks.

Professional citrus growers run the sprinklers all night when a hard freeze is expected.

I'm in the quilt group.
I wrap trees on frosty nights when they are young and small. Once a
lemon tree has been in the ground for at least three years, I no longer
try to protect it.

Winter lemon tree care is most critical when the plants are young. The older the tree gets, the tougher it will become--within reason. You will never be able to grow a lemon tree outdoors in zone six.

Also, the larger the tree
is, the more frost damage it can withstand. The new growth is most
vulnerable. That's why you shouldn't prune too late in the season. You
want the tree to go into winter somewhat overgrown.

Protecting the graft union.

Protecting the graft union is the most important part of lemon tree care. If this is damaged, you will lose the tree.

There
is normally a scar or bump on the trunk that will tell you where the
graft union is. On an unseasonably cold night, it is worth the trouble
to wrap this part of the trunk with a blanket or with lights.

The whole top of the tree can freeze. But if the graft union survives (and just a little wood above it) the tree will grow back.

On the other hand, if the graft union freezes, the tree may
grow back. But it won't be the same tree you had before. It will be
the rootstock variety which may not produce desirable fruit.

The
best solution to protecting lemon trees in winter is to plant a variety
of known to be hardy in your area. If you are at the edge of a tree's
hardiness zone, plant it in the warmest spot in your yard.

A southern exposure.

Under taller trees in high shade.

Beside a pond or lake.

Up against a building.

If you live above zone 9, the best solution is growing lemon trees in pots and moving them indoors before the first frost.Lemon
tree care is simple as long as you plant a hardy enough variety in a
warm enough location. Meyer lemon trees, being an orange/lemon hybrid,
have greater resistance to cold than most true lemons.

Growing Lemons as Houseplants

Bringing
the tree indoors during cold weather is the best winter lemon tree care
you could possibly provide. The tree will repay your kindness by
flowering and fruiting (if you hand pollinate it) at the same time just
to keep the winter blues at bay.